The objectives of this project are to examine the developmental aspects of bile acid metabolism in infants and children. The investigation will characterize the intraluminal phase of fat absorption and define bile acid kinetics in the normal fullterm and in premature infants by means of an isotope dilution technique, utilizing bile acids labeled with deuterium, a non-radioactive, stable isotope. Bile acid specific activity, or more exactly, the percent atoms excess, is determined by gas liquid chromatography-mass spectroscopy, at the Argonne National Laboratory. By this method it is possible to extend diagnostic and investigative procedures to infants and children, which due to radiation hazard, would have been previously denied. Knowledge of bile salt kinetics in the premature infant will provide a greater understanding of the mechanisms for inefficient fat absorption in the developing infant and provide a foundation for improving its overall nutritional status. The studies will be extended to include abnormal infants, infants with malabsorption, cystic fibrosis and cholestatic liver disease, for whom defects in bile acid synthesis or excretion play a major role. BIBLIOGRAPHIC REFERENCES: Watkins J.B., Szczepanik P., Gould J.B., Klein P.D., and Lester R.: Bile salt metabolism in the human premature infant: Preliminary observation of pool size and synthesis rate following the prenatal administration of dexamethasone and phenobarbital. Gastroenterology 69:706-713, 1975. Breslow J.L., Lothrop D.A., Spalding, D.R., and Watkins J.B.: Regulation of cholesterol metabolism in liver cell cultures. In Vitro 10:360, 1975.